JPS60146000A - Evaluation of crystal of silicon wafer and preparation of silicon ingot - Google Patents

Abstract

PURPOSE:To prepare the desired ingot by judging easily propriety of use, by forming an oxidized film on a silicon wafer made by single crystal pulling method, measuring pressure resistance of the oxidized film. CONSTITUTION:An oxidized film is formed by thermal oxidation on a silicon wafer obtained from a silicon ingot by single crystal pulling method. Pressure resistance of this oxidized film is measured, and in order to make the measured pressure resistance >= a certain value of pressure-resistant value of the highest frequency in terms of relationship between pressure resistance and frequency of a large number of measured results, a raw material of silicon polycrystal having higher purity, a crucible, a heater, an atmospheric gas are used. Further, single crystal, speed of rotation, and temperature profile of heating and cooling are properly controlled, so that a silicon ingot corresponding to use purpose of VLSI, etc. is prepared.

Description

Detailed Description of the Invention (7) Technical Field of the Invention The present invention relates to a method for evaluating silicon crystals (i.e., silicon wafer crystals) produced by a single crystal pulling method (hereinafter referred to as CZ method). 4, which relates to a method for manufacturing silicon ingots using the C2 method.
(a) Prior art In recent years, silicon devices have evolved from LSI to ultra-LSI, and in order to manufacture highly integrated and high-precision silicon devices at a high yield, it is necessary to increase the monthly yield of crystals. At the same time as improving quality, it is becoming necessary to understand and control small particles and defects in crystals. Along with this, crystal evaluation technology has also been developed. For example, Electronic Materials, February 1981 issue (Vol. 20. A 2),
Published by Kogyo Kenkyukai Co., Ltd., there is a special feature titled ``Innovative side slope/process evaluation J,'' in which silicon crystal δ-1-valence technology is introduced.

(1) Purpose of the Invention The present inventors have discovered that silicon crystals can be evaluated by measuring the withstand voltage (dielectric breakdown voltage) of thermal oxidation desorption on a silicon wafer. In particular, the breakdown voltage of a thermal oxide film is affected by heavy metal impurities (
For example, Al, Na.

It is an object of the present invention to estimate impurity emissions from the measurement of breakdown voltage. Conventionally, it has been possible to directly analyze these metal impurities using activation analysis, etc., but it is time-consuming and costly, and it is difficult to immediately determine whether or not the silicon wafer is a crystal that can be used for a specified purpose. was difficult. Another object of the present invention is to facilitate the determination of whether a silicon wafer can be used for a given purpose.

Furthermore, it is another object of the present invention to provide a method for manufacturing a silicon ingot by the C2 method, which becomes a silicon wafer that can be used for VLSI.

B) Structure of the Invention The above-mentioned object is to form an oxide film by thermal oxidation on a silicon wafer obtained from a silicon ingot made by the single crystal pulling (CZ) method, ) provides a method for evaluating silicon wafer crystals by measuring .

It is preferable to thermally oxidize the silicon wafer twice, and once
By removing the oxide film formed by the second thermal oxidation, the influence of the surface is eliminated, and the properties of the bulk crystal are reflected in the oxide film formed by the second thermal oxidation, and the breakdown voltage of that oxide film is measured.

Too bad, the present invention is based on the fact that the withstand voltage of a thermal oxide film formed on a silicon wafer obtained from a silicon ingot by the CZ method is the most frequent withstand voltage value in relation to the withstand voltage and frequency of a large number of measurement results on that wafer. In order to meet the above requirements, we provide high-purity silicon polycrystalline raw materials, crucibles, heaters, and x UL
++An object of the present invention is to provide a method for manufacturing a silicon ingot by appropriately controlling the rotational speed of a single crystal and a crucible and the temperature profile of heating and cooling using gas.
(3) Examples of the Invention The present invention will now be explained in more detail with reference to additional embodiments.

For example, the measurement of the breakdown voltage of the oxide film is performed as follows.

A single-crystal silicon ingot made by the usual CZ method is sliced into a number of silicon wafers, and each wafer is wrapped, perilled, and polished to produce a silicon wafer product. This silicon wafer is heated in a heating oxidation furnace, for example, at 1100°C, wet (98°C),
A 600 nm thick silicon dioxide (Sin) film is formed by humidified oxidation for 0 minutes. This 5i02 film is removed by etching. Next, the silicon wafer is
The material is dried and oxidized in a heated oxidation furnace, for example, at 1100° C., dry (hydrochloric acid added), for 20 minutes to form a 5 Q nm thick S+O. An aluminum evaporated film is formed on this Si02 film, and a large number of electrode patterns are formed by photo-etching. Is it possible to apply a voltage (for example, Lang voltage) to each of the electrodes formed in this way to insulate them? i
, @test to measure the breakdown voltage of the 5i02 film under the electrode.

Silicon wafer obtained from the TOP side of the silicon ingot (A) and silicon wafer obtained from TAIt[l+
When the breakdown voltage of the oxide film (Sin film) of B) was measured as described above, the results shown in FIG. 1 were obtained. If we take the oxide film breakdown voltage (V) on the horizontal axis of Fig. 1 and the frequency at that breakdown voltage (5. is indicated by a broken line B. As is clear from the figure, the frequency peak of the TOP side wafer (A) is the same as that of the TAIL 11 wafer (B).
It is on the higher voltage side than in the case of .

The breakdown voltage of the TOP side wafer is that much superior. From this, we can extract a suitable number of silicon wafers from the bottom of the TAIL side of the silicon ingot (for example, one by one) and measure the oxide film withstand voltage. If the result is determined and the result is at a certain predetermined level, the silicon wafer on the pTOP side can be used for a predetermined purpose (for example, for VLSI).

The F+ resistance of the thermal oxidation film of silicon wafers, metal impurities contained in silicon crystals (for example, Cu HA' T
It is also clear from the following experiment that the composition is affected by the following: (Na + Fe, Cr, Nt 1, etc.).

Experimental Example A P-type (100) silicon wafer (100 m) was prepared and heated in a dry oxygen (O2) atmosphere of 11'l.
Oxidize to form a 50 nm thick SiOz film. A metal impurity (copper) is introduced into the silicon wafer through this Sin film by ion implantation. This ion implantation was performed at an accelerating voltage of 100 KeV, and the dose profile was 1 x 10"c.
m-2,5X 10'4z- and l X J O"c
Perform this instead of m-2+. Next, after removing the Sin film by etching, it was thermally oxidized again in a dry oxygen (O2) atmosphere to a 50 nm thick 810. Forms a film.

An aluminum electrode is formed on this Sjoy film and a dielectric breakdown test is performed to measure the StO and withstand voltage of the film.

In this way, the results shown in FIG. 2 regarding copper impurities are obtained. It can be seen that the higher the amount of copper impurities in the silicon crystal, the lower the percentage of non-defective oxide films with breakdown voltage (that is, the number of silicon crystals with low breakdown voltage) decreases.

From the above, the silicon wafer's oxide film has a high breakdown voltage, and its crystals contain fewer metal impurities.
The quality of the crystal, that is, whether it has crystallinity that can be used for a given purpose can be determined by measuring the withstand pressure.

Furthermore, in order to improve the oxide film breakdown voltage, in other words, in order to make the most frequent breakdown voltage value equal to or higher than a certain value (for example, 9MV/+n) in relation to the breakdown voltage and frequency of each silicon wafer, silicon In the production of ingots, it is sufficient to use a highly purified silicon polycrystalline raw material, a nodotsu pot, a heater, and a gas atmosphere, and to appropriately control the rotational speed of the single crystal to be pulled and the crucible, as well as the temperature profile of heating and cooling. , (7) Effects of the invention As mentioned above, by measuring the breakdown voltage of the thermal oxide film of a silicon wafer, the wafer can be easily used for a specified purpose (ultra-L).
It becomes possible to determine whether the crystal can be used for SI manufacturing.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the resistance n-5 of the thermal oxide film of a silicon wafer and the frequency number, and Figure 2 shows the relationship between the copper impurity level in the silicon wafer and the oxide film breakdown voltage non-defective rate. It is a line diagram showing a relationship. Patent applicant Fujitsu Limited Patent agent Akira Aoki Patent attorney Kazuyuki Nishidate Patent attorney Yukio Uchida Patent attorney Akira Yamaguchi 8151 Figure 2 Copper ion implantation amount

Claims (1)

[Claims] 1. The crystal of the silicon wafer is obtained by forming an oxide film by thermal oxidation on a silicon wafer obtained from a silicon ingot made by the single crystal pulling method, and measuring the breakdown voltage of this oxide film. How to evaluate. 2. The breakdown voltage of the thermal oxide film formed on a silicon wafer obtained from a silicon ingot by the single crystal pulling method is greater than or equal to the highest frequency breakdown voltage value based on the relationship between the breakdown voltage and frequency of numerous measurements on that wafer. A method of manufacturing silicon ingots using high-purity silicon polycrystalline raw materials, a crucible, a heater, and atmospheric gas, and by appropriately controlling the rotational speed of the single crystal and crucible and the temperature profile of heating and cooling, so that .